Semi-useless comment here, but just noting that we also have had a bit of that same grayish bubbly film on and off over the past month now that it's gotten hot. Our pond is non-aerated, so the bubbles aren't purely aeration bubbles. This all coincided with the warmer temps, and what was previously extremely clear water with plenty of FA has now turned between olive green to slightly brown with much lower visibility and very little FA.

I'm thinking it's some kind of phytoplankton bloom (I hope at least), though I also wonder if it has to do with pellet feeding pretty heavily (the oily looking patches I would naively blame on uneaten pellets).